1. Field of the Invention
The present invention relates to an air conditioner with a dual function of the cooling and heating operations, and more particularly to a defrosting apparatus of an air conditioner and method thereof to correctly discriminate whether frost has accumulated at an outdoor unit.
2. Description of the Prior Art
A general air conditioner includes a heating apparatus for supplying warm air by heating cold room air and a cooling apparatus for supplying cool air by cooling warm room air. Besides, a heating or cooling apparatus is also marketed for a dual function of heating and cooling operations and for air purifying function which cleans the polluted room air.
FIGS. 1 and 2 illustrate an indoor unit of the heating or cooling apparatus (generally referred to as an air conditioner) among conventional air conditioners. As shown in FIG. 1, an suction grille member(5) is provided at a lower front surface of an indoor unit main body (hereinafter referred to as a main body) with a plurality of suction inlets(3) to suck room air and with a plurality of discharge outlets(7) at an upper front surface of the main body to discharge the heat-exchanged air, i.e., the heated or cooled air, that is sucked through the suction inlets(3).
Furthermore, the discharge outlets(7) comprises horizontal vanes(9) and vertical vanes(11) for controlling the vertical and horizontal directions of the air discharged indoors therethrough(7), a covering member(13) attached for forming an external appearance thereof and for protecting interior parts therein, and an operating part(15) disposed at a lower portion of the cover member(13) for controlling overall operational modes (automatic, cooling, dehumidifying, blow, heating, etc.) of the air conditioner, a start or stop operation thereof and the amount and direction of the air discharged through the discharge outlets(7).
As shown in FIG. 2, there are provided a filtering member(17) disposed at an inner side of the suction grille member(5) for filtering dust and foreign objects floating with the room air sucked through the suction inlets(3) and an indoor heat-exchanger(19) disposed in the filtering member(17) for heat-exchanging heated air or cooled air through evaporative latent heat of a coolant.
In addition, the heat-exchanger(19) is disposed thereover with a blower fan(23) (hereinafter referred to as indoor fan) which rotates according to operation of an indoor fan motor in order to suck the room air through the suction inlets(3) and, at the same time, to discharge through the discharge outlets(7) the air heat-exchanged at the heat-exchanger(19). The indoor fan(23) is also provided with a duct member(25) at an external side thereof for covering the indoor fan(23) and for guiding the flow of the air sucked through the suction inlets(3) and discharged through the discharge outlets(7).
In an inverter air conditioner with a dual function of the heating and cooling operations, the four way valve(31) is turned on for the heating operation and thereby the coolant is circulated in the following sequence: compressor(39)--four way valve(31)--indoor heat-exchanger(19)--expansion valve(33)--heating expansion valve(34)--outdoor heat exchanger(35)--four way valve(31)--compressor(39), as shown in the dotted line in FIG. 3.
On the other hand, when the four way valve(31) is turned off for the cooling operation, the coolant circulates in the following sequence: compressor(39)--four way valve(31)--outdoor heat-exchanger(35)--one way valve(36)--expansion valve(33)--indoor heat-exchanger(19)--four way valve(31)--compressor(39) as shown in the straight line in FIG. 3. At this time, the four way valve(31) controls the circulation route of the coolant in the straight line or in the dotted line respectively when the four way valve(31) is turned off or on.
In the inverter air conditioner with a dual function of the cooling and heating operations, an user turns on a start/stop key (hereinafter referred to as an operation key) with a remotely controlled unit or with the operating part(15) and selects a desired operation mode (for instance, heating). When the set temperature(Ts) is higher than the room temperature (Tr), an operation frequency of the compressor(39) is determined according to a temperature difference between Ts and Tr to drive the compressor(39).
When the compressor(39) is driven, the coolant is circulated in the following sequence, as shown in the dotted line in FIG. 3: compressor(39)--four way valve(31)--indoor heat-exchanger(19)--expansion valve(33)--heating expansion valve(34)--outdoor heat-exchanger(35)--four way valve(31)--compressor (39), thereby heating the indoor heat-exchanger(19). Operation of the indoor fan(23) is controlled according to the temperature of the indoor heat-exchanger(19).
If the temperature of the indoor heat-exchanger(19) is lower than the predetermined temperature (about 27.degree. C.), the indoor fan(23) is stopped to prevent cool air from being discharged indoors at the initial heating stage. If the temperature of the indoor heat-exchanger(19) is higher than the predetermined temperature (about 27.degree. C.), the indoor fan(23) is operated.
If the indoor fan(23) is rendered operative, the dust and foreign objects floating in the room air sucked through the suction inlets(3) into the main body(1) are removed by the filtering member(17). The purified room air is heat-exchanged into warn air by way of evaporative latent heat of the coolant at the indoor heat-exchanger(19).
The warm air heat-exchanged at the indoor heat exchanger(19) is guided upwards and discharged indoors through the discharge outlets(7). The warm air discharged through the discharge outlets(7) carries out the heating operation at air directions according to the angles of the vanes(9) and (11).
If the heating operation is carried out for a certain period of time and the air blown from outside is heat-exchanged and cooled by evaporative latent heat at the outdoor heat-exchanger(35), frost can be accumulated at the outdoor heat-exchanger by the cool air being discharged outside. Therefore, there is a problem in that the accumulated frost turns into thick ice, thereby deteriorating the operation efficiency of the outdoor heat-exchanger(35) and increasing energy consumption. In addition, there is another problem in that the frost accumulated on the outdoor heat-exchanger(35) causes ice formation phenomenon, resulting in an operation defect at the compressor(39).
As for these problems, the conventional air conditioner includes a pipe temperature sensor (not shown) which detects the temperature of the outdoor heat-exchanger(35) from 30 minutes after the compressor(39) has started being operated during the heating operation, to thereby measure the temperature changing speed of the outdoor pipe temperature. If the temperature changing speed of the outdoor pipe temperature is over the predetermined speed, it is regarded as a frosting condition where the frost has accumulated. Therefore, an outdoor fan(37) and an indoor fan(23) are stopped to cease the heating operation, and the four way valve(31) is turned off to convert the operation of the air conditioner into the cooling operation.
Accordingly, the coolant is circulated in the following sequence for the cooling operation: compressor(39)--four way valve(31)--outdoor heat-exchanger(35)--one way valve(36)--expansion valve(33)--indoor heat-exchanger(19)--four way valve(31)--compressor(39), to thereby start heating the outdoor heat-exchanger(35) for removing the frost accumulated on the outdoor heat-exchanger(35).
However, there are problems in the conventional defrosting method of the air conditioner in that a rapid measurement of the temperature changing speed at the outdoor heat-exchanger(35) and a high precision of the pipe temperature sensor (not shown) are necessary to detect a frosting condition, thereby increasing the cost of the high precision product and bringing about inaccurate detection about the accumulated frost on the outdoor unit as the temperature of the outdoor heat-exchanger(35) is detected.